Hydraulic filter assembly with priority valve

ABSTRACT

A filter module assembly utilizes a priority valve installed in a manifold to allow for continuous filtration of hydraulic fluid up to a predetermined flow value and diverts occasional high flow to a secondary circuit. This arrangement provides both a low pressure drop at a high flow condition and structural integrity (1,000,000 impulse cycles from 0 to 6000 psi) while at the same time may reduce the weight by as much as 50% from a conventional design approach.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention generally relates to fluid filtration. Moreparticularly, the present invention relates to a filter assembly forhigh pressure, high flow rate and low pressure drop applications.

2. Discussion of the Related Art

Fluid cleanliness and viscosity are two important properties ofhydraulic fluid in a fluid power system. Contaminants may be supplied tothe hydraulic system from sources both internal and external to thesystem. The level of undesirable contaminants in the hydraulic fluidaffects the quality of system performance, as well as the useful life ofsubstantially all of the working hydraulic components within a hydraulicsystem. All moving components in contact with the fluid are vulnerableto wear, and attendant premature failure if such contaminants are notremoved from the system. Consequently, proper cleaning of the fluid toremove undesirable contaminants can significantly lengthen the life ofthe system components, as well as reduce maintenance and its attendantcosts. Further, effective cleanliness control can result in significantimprovements in the overall reliability and performance of the system.

Maintenance of a clean hydraulic fluid requires efficient filtration. Anumber of methods have been utilized to control the cleanliness of thefluid in hydraulic systems. The filters utilized in typical cleanlinesscontrol systems must withstand high pressure and/or high volume flow incertain applications. Consequently, such filter arrangements are oftenexpensive and can contribute to related system problems.

Higher demands are made upon the hydraulic systems of aircraft.Microscopic particles present a significant problem because it isdifficult to manufacture a filter element that is capable of removingvery small particles and at the same time has a sufficient flow capacityand low pressure drop to meet the flow requirements of typical aircraftsystems.

The flow capacity of a filter is a function of the surface area andmicron removal rating. Aircraft have limited space and weightrequirements. It is difficult to manufacture a filter element that iscapable of removing fine particles, has a high flow capacity, a lowpressure drop, is small in size, and is rugged enough for aircrafthydraulic systems.

For example, a filter may be interposed in line before the load toprovide full flow filtering. This method is effective in many types ofsystems having relatively low fluid flow, e.g., 30 gallons per minute(gpm) or less. However, many hydraulic systems provide relatively largeflows at high pressures, often running on the order of 400 gpm atpressures of 1000 pounds per square inch (psi) or greater. Interposing afilter in line before the load is often impractical in those highpressure systems with relatively large fluid flows. Further, maintainingfilters in such an environment is generally quite expensive.

Alternately, full flow filtering may be provided after fluid hasserviced the load. In this method of filtering, a filter is typicallyinterposed in the return line between the load and the sump. Althoughless costly than filtering systems having the filter disposed before theload, return oil filtering can still be quite costly. Additionally, asreturn line filters become dirty, they develop back pressure. Thedevelopment of back pressure can be a problem in that a number ofvalving systems do not perform properly with the application of backpressure.

An additional method of filtering disposes a filter in the sump. Bynature, these filters are coarse so as not to affect flow of fluid tothe pump. Consequently, while this method may be effective for filteringlarge particles, small particles are not effectively blocked.

Engine oil lubrication systems, which are typical of many fluid systems,frequently include a filter assembly which has a filter formed from aporous filter medium for removing damaging particles from thelubricating oil utilized in the system. Mechanical wear within theengine, the outside environment, and contaminants accidentallyintroduced during normal servicing provide a source of large particleswhich may plug lubricating nozzles or severely damage parts and createexcessive wear on any surfaces relying on a thin film of the lubricatingoil for protection.

These systems typically rely upon a pump to force the oil through thefilter and then circulate the filtered oil to the moving parts of theengine for lubrication. Oil is forced through the filter by limitedpressure developed on the upstream side of the filter by the oil pump.The pressure required to force oil to pass through the filter at a givenrate will be greater for more viscous or thick oils or for filtersformed from finer pored filter media, i.e., porous filter media havingsmaller average or mean pore diameters.

Viscosity is a measure of the resistance of the fluid to flow, or, inother words, the sluggishness with which the fluid moves. When theviscosity is low, the fluid is thin and has a low body; consequently,the fluid flows easily. Conversely, when the viscosity is high, thefluid is thick in appearance and has a high body; thus, the fluid flowswith difficulty.

Oil is generally thicker or more viscous at low temperatures and thus,when an engine is started and the engine parts and oil are cold, alarger pressure is required to force the oil through the filter thanafter the engine has reached operating temperature. Since the pumpfrequently has limited pressure capabilities, many systems include abypass valve, which will open when the pressure exceeds a predeterminedvalue and allow oil to bypass the filter. This results in unfiltered oilbeing pumped through the engine where large particles may harm themoving parts and clog passages. Further, the high upstream pressuredeveloped during a cold start may cause the lighting of a high pressureoil light, erroneously indicating that the filter is dirty or that thelubrication system is otherwise obstructed.

Automatic self-compensating flow control lubrication systems forcontinuously supplying the requisite amount of lubricant to at least onemoving component of a drive system are known in the art. Variousapplications require that fluid condition in a mechanical system becontinuously monitored and adjusted to maintain optimum overall systemperformance.

Present lubrication systems of the type used, for example, in drivesystems for gas turbine engines are designed to supply a near constantoil pressure to fixed jets in the various engine components whichrequire lubrication including bearing package, gears and the like.Systems such as this are designed to supply the minimum flow requiredfor the worst case. This philosophy inevitably leads to excessive flowconditions in most other engine operating modes. Deteriorating systemconditions, such as clogging jets, cannot be corrected and requireoperator attention with the possibility of mission cancellation.

In addition to the primary flow functions of the system, presentconfigurations include some diagnostic and condition monitoringprovisions. However, these are mainly warning lights and/or gages, whichrequire crew attention and only add to the operator workload.

One such system is disclosed in U.S. Pat. No. 5,067,454 (“the Waddingtonet al. reference”). The disclosed invention relates to an automatic selfcompensating flow control lubrication system. One or more operatingparameters, such as scavenge temperature, are continuously monitored andthe information provided to a computer. The computer operates the firststage solenoid valve of a two stage valve assembly which provides suchan amount of lubricant to the component as is necessary to maintain apredetermined value of the operating parameter. Scavenge temperature isone such operating parameter.

In the operation of this lubrication system, oil or other suitableliquid lubricant, is drawn from a reservoir by means of a suitable pumpthrough a replaceable filter assembly which incorporates a controlledbypass valve which, together with the filter assembly is an integralpart of the pump assembly. The bypass valve allows essentially dirty oilto be supplied to the components of the drive system requiringlubrication in emergency situations during which the filter is clogged.Alternatively, it operates to continue flow of oil during cold weatherstarting when the oil is too viscous to pass through the filter.

A computer controlling operation of the lubrication system controlswhether and when the bypass valve opens. Other similar prior art systemsopen and close the bypass valve at fixed points, which have the effectof reducing filter life. The Waddington reference, by opening the bypassvalve only when absolutely necessary, increases filter life and life ofthe drive system by reducing the time that dirty oil is supplied to thecomponents requiring lubrication.

U.S. Pat. No. 4,783,271 (“the Silverwater reference”) discloses a filterassembly which removes particles from a fluid and which comprises twofilters and a structure for directing the fluid first through one filterand then through the other. Each filter includes a porous filter medium.However, the filter medium of the downstream filter is coarser than thefilter medium of the upstream filter, i.e., the mean pore diameter ofthe porous filter medium of the downstream filter is greater than themean pore diameter of the porous filter medium of the upstream filter.

The filter assembly further includes a mechanism for sensing thetemperature of the fluid and a valve, which is responsive to thetemperature-sensing mechanism. The valve is arranged in parallel withthe upstream filter so that, when the fluid temperature reaches apredetermined value as sensed by the sensing mechanism, the valve opens,allowing the fluid to bypass the upstream filter and flow through thecoarser downstream filter. For example, in one embodiment of theinvention, the valve is open when the fluid temperature is below thepredetermined value.

With the filter assembly according to the Silverwater reference, thefluid is always filtered, regardless of the temperature of the fluid.When the fluid temperature increases, e.g., approaches the normaloperating temperature, and reaches a predetermined value, as sensed bythe sensing mechanism, the valve closes, causing all the fluid to flowthrough both filters. Thus, the finer upstream filter removes allparticles from the fluid while the coarser downstream filter serves as abackup filter in case the upstream filter is damaged or defective.

However, when the temperature of the fluid, as sensed by the sensingmechanism, falls below the predetermined value, e.g., falls below apredetermined lower limit when the engine is shut down, the valve opens.Consequently, when the engine is next started, the fluid partiallybypasses the upstream filter but all of the fluid is passed through thecoarser downstream filter.

The downstream filter may frequently be physically smaller than theupstream filter. Therefore, in order to minimize the obstruction to flowby the downstream filter when filtering cold, viscous oil, thedownstream filter preferably has a much larger mean pore diameter thanthe upstream filter. However, the mean pore diameter of the downstreamfilter is nonetheless small enough that the filtration provided by thedownstream filter is sufficient to remove any large particles which mayhave been introduced into the fluid.

The size and the weight of a filter assembly are major factors inhydraulic system design, especially in aerospace applications. Thesedemands, coupled with the further requirements of low pressure drop,high flow rates and improved fatigue life at continually increasingoperating pressures, require departure from the standard design approachin hydraulic systems.

Therefore, there is a need for an innovative approach in the design of ahigh pressure hydraulic filter module, which provides both the requiredperformance (low pressure drop at a high flow condition) and thestructural integrity (1,000,000 impulse cycles from 0 to 6000 psi) andat the same time reducing the weight by as much as 50% from aconventional design.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A illustrates a pressure filter module assembly with a priorityvalve according to an embodiment of the present invention;

FIG. 1B illustrates a return filter module assembly with a priorityvalve according to an alternative embodiment of the present invention;

FIG. 2 illustrates conventional approach utilizing two filters;

FIG. 3A illustrates an assembly drawing of a priority valve according toan embodiment of the present invention;

FIG. 3B illustrates a priority valve in the closed position relative tothe secondary outlet according to an embodiment of the presentinvention;

FIG. 3C illustrates a priority valve in the open position relative tothe secondary outlet according to an embodiment of the presentinvention;

FIG. 4A illustrates a pressure manifold housing according to anembodiment of the present invention;

FIG. 4B illustrates a return manifold housing according to analternative embodiment of the present invention;

FIG. 5 illustrates a pressure filter bowl according to an embodiment ofthe present invention;

FIG. 6A illustrates a filter element according to an embodiment of thepresent invention;

FIG. 6B illustrates a filter media according to an embodiment of thepresent invention;

FIGS. 7A-7D illustrate various views of the pressure filter moduleassembly with a priority valve according to an embodiment of the presentinvention;

FIG. 8A illustrates a schematic drawing of the pressure filter moduleassembly with a priority valve according to an embodiment of the presentinvention; and

FIG. 8B illustrates a schematic drawing of the return filter moduleassembly with a priority valve according to an alternative embodiment ofthe present invention.

DETAILED DESCRIPTION

Advancement in hydraulic systems in the 4000+psi operating rangerequires an innovative filter design approach to meet the highperformance requirements, i.e., low pressure drop at a high flowcondition, structural integrity (1,000,000 impulse cycles from 0 to 6000psi.), and reduced size and weight. To meet these requirements using astandard approach would require a filter element or elements with anexcessive amount of media area. This in turn will make the filterassembly extremely large, very heavy, and structurally unsound, oralternatively, require two filter assemblies.

FIG. 1A illustrates a high pressure filter module assembly 100 that may,for example, be interposed in a line before a load to provide full flowfiltering. Filter module assembly 100 may include a high pressuremanifold 130, a disposable primary filter element 110, and a highpressure filter bowl 120 which is liquid-tightly connected at one end tothe high pressure manifold 130 and is closed at the other end. The highpressure manifold 130 may include a fluid inlet passage 140, a fluidoutlet passage 145, a priority valve 150, a disposable secondary filterelement 115, and a high pressure relief valve 156. In addition, filtermodule assembly 100 may include a prognostic and health monitoringdevice 160 to measure pressure, temperature and flow.

Under normal flow operating conditions, the flow enters the highpressure manifold 130 through the fluid inlet passage 140. The priorityvalve 150 allows the flow, for example up to 40 gpm, to enter theprimary circuit (flow through the primary filter element 110), and flowout through the fluid outlet passage 145.

During peak flow conditions when the flow demand exceeds 40 gpm, thepriority valve 150 directs flow in excess of 40 gpm, for example up to160 gpm, to the secondary circuit (flow through the secondary filter115) and out through the fluid outlet passage 145.

FIG. 1B illustrates an alternative embodiment of the present invention.A return filter module assembly 101 is also designed for low pressuredrop at a high flow condition, but is used at lower pressure and impulselevels. The return filter module assembly 101 may, for example, beinterposed in a return line between the load and a sump. Return filtermodule assembly 101 may include a return manifold 131, a disposableprimary filter element 110, and a return filter bowl 121 which isliquid-tightly connected at one end to the return manifold 131 and isclosed at the other end. The return manifold 131 may include a fluidinlet passage 140, a fluid outlet passage 145, a priority valve 150, anda disposable secondary filter element 115. The return filter moduleassembly 101 may include a bypass valve 155. In addition, return filtermodule assembly 101 may also include a prognostic and health monitoringdevice 160 to measure pressure, temperature and flow.

The high pressure filter module assembly 100 utilizes the priority valve150 installed in the high pressure manifold 130 to allow for continuousfiltration of the hydraulic fluid up to a predetermined flow value (e.g.up to 40 gpm) and diverts the occasional high flow to the secondarycircuit. This approach provides both the required performance (lowpressure drop at a high flow condition) and the structural integrity(1,000,000 impulse cycles from 0 to 6000 psi) and at the same time mayreduce the weight by as much as 50% from a conventional design approach.

FIG. 2 illustrates a conventional design approach that requires twofilter assemblies combined in parallel as shown in the schematicdrawing. Two filters are required to meet the required performance (lowpressure drop at a high flow condition) and the structural integrity(1,000,000 impulse cycles from 0 to 6000 psi).

The filter design including the priority valve 150 is based on theobservation that in certain applications, the normal flow requirement ina system may be, for example 40 gpm, with only occasional peak flows upto 200 gpm. In more defined terms, it may be that the peak flow of 200gpm occurs during 5% of the operational time of an aircraft and a flowup to 100 gpm occurs less than 15% of the time. The remaining 80% of thetime the flow is no greater than 40 gpm.

Based on this understanding, the pressure filter module assembly 100provides continuous filtration of 40 gpm (primary circuit) and allowsfor the bypassing of any excess flow, up to 160 gpm (secondary circuit),through a priority valve 150. The excess flow is filtered through aparallel secondary filter 115. The primary and secondary filters form aparallel combination to provide for a lower pressure drop as compared toa series combination of two filters.

It should be understood that the two scenarios 1) 200 gpm- (40 gpmfiltered and 160 gpm bypassed), and 2) 100 gpm (40 gpm filtered and 60gpm bypassed) will still maintain the oil integrity to ensure peakperformance. The bypassing of the flow does not degrade the performanceof the hydraulic circuit or associated components because of itsrelative short duration and secondary filtration.

The purpose of the priority valve 150 is to guarantee that all availableflow up to a predetermined flow (e.g. 40 gpm) will go to a primary(priority) circuit, including the primary filter 110. Any excess flow(e.g. up to 160 gpm) will be diverted to a parallel secondary circuit.This parallel secondary flow or excess flow is filtered through a moreopen higher micron rating filter 115 before the fluid exits through theoutlet 145. One common inlet 140 and outlet 145 is used for bothcircuits eliminating the need for additional plumbing.

The return filter module assembly 101 also utilizes a priority valve 150installed into a return manifold 131 that allows for continuousfiltration of the hydraulic fluid up to a predetermined flow value (e.g.up to 40 gpm) and diverts the occasional high flow to a secondarycircuit.

FIG. 3A illustrates the priority valve 150 according to embodiments ofthe present invention. Priority valve 150 includes a valve body 300,first circular apertures 301, second circular apertures 302, meteringorifice 310, end fitting 320, piston assembly 330 including a firstcylindrical portion 332 and second cylindrical portion 333 containingcircular apertures 331, retainer 340, spring 350, and spring guide 360.

With reference to FIG. 3A and FIG. 3B, the piston assembly 330 isslidably mounted within the valve body 300, the spring 350 being biasedin a first shape in contact with the spring guide 360 urging the pistonassembly 330 into a first position within the valve body 300 to closethe first cylindrical portion 332 of the piston assembly 330 over theplurality of first circular apertures 301 of the valve body 300 when theflow rate of a fluid is below a predetermined fluid flow rate.

Furthermore, with reference to FIG. 3A and FIG. 3C, the spring 350 beingbiased in a plurality of shapes in contact with the spring guide 360allowing the first cylindrical 332 portion of the piston assembly 330 tomove away from the first position to allow the first cylindrical portion332 of the piston assembly 330 to expose the plurality of first circularapertures 301 of the valve body 300 when the flow rate of the fluid isabove a predetermined fluid flow rate, the plurality of first circularapertures 301 of the valve body 300 then being in communication with afirst passage 306 (see FIG. 3C) to form a fluid pathway secondarycircuit, the plurality of spring 350 shapes and the amount of exposureof the plurality of first circular apertures 301 of the valve body 300is proportional to the flow rate of the fluid. The exposure of theplurality of first circular apertures 301 of the valve body 300 definesthe second piston metering land.

FIG. 3B illustrates that when the priority valve 150 is initiallyclosed, flow is directed through the primary circuit, from primary inlet140 to the primary outlet 146, and the secondary circuit is closed offThe pressure drop across the metering orifice 310 in the piston assembly330 is not high enough to overcome the installed spring 350 force,therefore the piston assembly 330 remains in the first position withinthe valve body 300. In this position the plurality of first circularapertures 301 in the valve body 300 are not exposed and thus the secondpiston metering land (the exposure of the circular apertures 301 in thevalve body 300 by the piston assembly 330) is closed preventing flow tothe secondary circuit. All flow will be ported to the primary circuitthrough the plurality of circular apertures 331 in the secondcylindrical portion 333 of the piston assembly 330 and the secondcircular apertures 302 in the valve body 300.

FIG. 3C illustrates that as the flow to the primary circuit increases,the pressure drop across the metering orifice 310 in the piston assembly330 overcomes the installed spring 350 force forcing the piston assembly330 downward away from the first position within the valve body 300 toexpose the plurality of first circular apertures 301 in the valve body300. This opens the second piston metering land, and bypasses the excessflow to the secondary circuit. If the primary flow across the fixedorifice 310 decreases below the set gpm rating, the spring 350 biasforce will close off the secondary piston metering land to assure allthe flow available will be ported to the primary circuit through theplurality of circular apertures 331 in the second cylindrical portion333 of the piston assembly 330 and the second circular apertures 302 inthe valve body 300. (Refer back to FIG. 3B.)

FIG. 4A illustrates a high pressure manifold 130 according to anembodiment of the present invention. The high pressure manifold 130 maybe constructed from anodized titanium material TI-6AL-4V. The use oftitanium is recommended because of the filter modules specification andperformance requirements. Due to the relatively large size, high pumpdischarge pressure levels and the stringent qualification impulserequirements, titanium provides the best strength to weight ratio overother material options.

Previous experience dictates that for high pressure systems and severeimpulse requirements (1,000,000 cycles from 0 to 6000 psi) the use oftitanium is necessary to ensure the success of the qualification whilestill providing a product with the least weight. In an alternativeembodiment of the present invention, the high pressure manifold 130 maybe manufactured using Precipitation Hardened Stainless Steel bar 15-5PH.

FIG. 4B illustrates the return manifold 131 according to an alternativeembodiment of the present invention. The return filter manifold 131 maybe manufactured using anodized 7075-T7351 aluminum or 2024-T851aluminum.

FIG. 5 illustrates the high pressure filter bowl 120 according to anembodiment of the present invention. The high pressure filter bowl 120is constructed from TI-6AL-4V. The bowl achieves the desired fatiguelife of the high pressure manifold 130. The high pressure filter bowl120 houses the primary filter element 110 and is removable forreplacement of the primary filter element 110.

The return filter bowl 121 (not shown) is the same size and shape as thehigh pressure filter bowl 120. The return filter bowl 121 may bemanufactured using anodized 7075-T7351 aluminum or 2024-T851 aluminum.The return filter bowl 121 also houses the primary filter element 110and is removable for replacement of the primary filter element 110.

The high pressure filter bowl 120 and return filter bowl 121 may beinstalled and tightened by hand. Both filter bowls 120, 121 include aknurled friction pad for this purpose. No other equipment, fitting, etc.is required to remove or disconnect the bowl and its respective elementfor servicing/maintenance. In the event that hand torque is not adequatefor bowl removal, a wrenching pad 510 is provided at the bottom of eachbowl. This design allows removal of the bowl with standard tools, butdoes not allow over torquing. The pitch diameters of the bowl threads520 are modified to preclude false installation of the similarly sizedand shaped pressure and return bowls. The high pressure filter bowl 120may be secured to the high pressure manifold 130 with lockwire.Alternatively, a more maintenance friendly locking lever can also beprovided if required.

FIG. 6A illustrates the primary filter element 110 according to anembodiment of the present invention. Multi-layered filter media providesoptimum filtration capability. The primary filter element 110 is a highpressure high collapse (in this case 6000 psi) filter element. Referringto FIG. 6B, the media pack assembly 600 is the core of the primaryfilter element 110. The media pack 600 may consist of four or morelayers of porous material.

The outer layer 610, a corrosion resistant steel (CRES) mesh, is forprotection during handling. The second layer 620 is the actual filtermedia that provides the filtration efficiency and retained dirtcapacity. It may consist of an epoxy modified phenolic resin impregnatedglass fiber matrix. The third layer 630 provides flow distribution andis used to support the media. All additional layers 640 are to furthersupport the media pack as needed. These layers are pleated, formed intoa cylinder to maximize the filter area then side sealed with epoxy.

The center tube assembly (not shown) consists of a tube and a wire meshcylinder. The tube is a rolled and butted perforated sheet, with thehole-pattern, thickness and material designed to meet the requiredpressure drop and collapse strength (some high pressure applications usecylinder wire “slinky”). The cylinder of CRES wire mesh is wrappedaround the center tube to prevent the pleated pack assembly from pushingthrough the holes in the perforated center tube at high differentialpressure. Filter element fittings and end caps are machined or stampedfrom 300 series CRES and passivated.

At assembly, the tube assembly is inserted into the media pack assembly600 which are in turn attached to the fitting and end cap with asuitable adhesive. All materials and adhesives used in the filterelement assemblies have been shown through testing to be fully effectivefor filtering fluids over the entire fluid temperature range of −65° F.to +275° F. (i.e. in this case MIL-PRF-83282 and MIL-PRF-87257).

FIGS. 7A-7D illustrate various views of the pressure filter moduleassembly according to an embodiment of the present invention. Theenvelope of the module may be as small as 23.1 inch×10.1 inch×9.95 inch.The calculated dry weight of the pressure filter assembly may be aslight as 70.0 lb. The high pressure manifold 150 may be equipped withinlet 710 and outlet 720 sensors that allow for continuous monitoring ofpressure, temperature and flow.

In an alternative embodiment of the present invention, the return filterassembly (not shown) may be as small as 22.5 inch×8.5 inch×9.95 inch,and may have a lower calculated dry weight of 48.0 lb maximum (due tothe use of aluminum for the manifold and bowl).

A system schematic of the pressure filter module assembly 100 and returnfilter module assembly 101 are shown in FIGS. 8A and 8B, respectively.The schematics illustrate the various flow paths and the associatedcomponent locations. Under normal flow operating condition, the flowenters the manifold through the inlet port 810. The primary circuitallows flow up to 40 gpm to enter the primary filter element 110 andflow out through a check valve 815 (which serves also as an outletshutoff valve) to the outlet port 820.

During peak flow conditions when the flow demand exceeds 40 gpm, apriority valve 150 in the module directs flow in excess of 40 gpm up to160 gpm, to the secondary circuit through a secondary filter 115 and outthrough a common outlet port 820.

FIG. 1A and FIG. 8A illustrates the pressure filter module assembly 100may include a high-pressure relief valve 156 provided downstream of theprimary filter element 110 and secondary filter element 115 to relievethe flow, up to 200 gpm, through the relief valve outlet port 157 incase of a system problem (valve malfunctions downstream causingpotential catastrophic increase of system pressure) downstream of thepressure filter module assembly 100.

FIG. 1B and FIG. 8B illustrates the return filter assembly 101 mayinclude a bypass valve 155 in parallel with the primary filter element110 to allow bypassing of the primary flow, up to 40 gpm, to the outletport 820 in the case of filter element blockage.

While the description above refers to particular embodiments of thepresent invention, it will be understood that many modifications may bemade without departing from the spirit thereof The accompanying claimsare intended to cover such modifications as would fall within the truescope and spirit of the present invention. The presently disclosedembodiments are therefore to be considered in all respects asillustrative and not restrictive, the scope of the invention beingindicated by the appended claims, rather than the foregoing description,and all changes that come within the meaning and range of equivalency ofthe claims are therefore intended to be embraced therein.

1. A filter module assembly for removing particles from a fluid, thefilter module assembly comprising: a manifold housing having an inletfor receiving the fluid to be filtered, an outlet for expelling thefluid, and fluid flow paths therebetween, said manifold housing beingattached atop a filter bowl; a parallel combination of a first filteringelement contained within said filter bowl and a second filtering elementcompletely contained within said manifold housing, each having a porousfilter medium; and a fluid flow rate responsive valve arranged incommunication with the inlet, the first filtering element, and thesecond filtering element, said valve being activated when a fluid flowrate through the inlet increases above a predetermined threshold value,the amount of fluid above said threshold value being diverted away fromsaid first filtering element and through said second filtering elementwhile the amount of fluid at and below said threshold value continues topass through said valve to said first filtering element, said valvebeing contained completely within the manifold housing and not in directcommunication with the outlet or a downstream side of the firstfiltering element, wherein fluid filtered in said first filteringelement and fluid filtered in said second filtering element is expelledthrough said outlet.
 2. The filter module assembly of claim 1 whereinthe filter medium of at least one of the filtering elements is pleated.3. The filter module assembly of claim 1 wherein the filter medium of atleast one of the filtering elements has a hollow, generally cylindricalconfiguration.
 4. The filter module assembly of claim 1 wherein thefilter module assembly includes a high pressure relief valve.
 5. Thefilter module assembly of claim 1 wherein the filter module assemblyincludes a bypass valve.
 6. The filter module assembly of claim 1wherein the filter module assembly includes a device to measurepressure, temperature, and flow.
 7. A filter module assembly comprising:a manifold housing having an inlet for receiving a fluid to be filtered,an outlet for expelling the fluid, and fluid flow paths therebetween,said manifold housing being attached atop a filter bowl; a primaryfiltering element and a secondary filtering element positioned inparallel to define a primary circuit fluid flow path and a secondarycircuit fluid flow path respectively, the primary filtering elementbeing contained within the filter bowl, the secondary filtering elementbeing contained completely within the manifold housing, each filteringelement including a porous filter medium, a mean pore diameter of theporous filter medium of the primary filtering element being smaller thana mean pore diameter of the porous filter medium of the secondaryfiltering element; and a fluid flow rate responsive valve forselectively directing at least a portion of the fluid away from theprimary filtering element and through the parallel secondary filteringelement, said valve including: a piston including a metering orifice, aspring, and a valve body, said valve being activated when a fluid flowrate through the inlet increases above a predetermined fluid flow rate,said piston moving relative to said valve body to allow the amount offluid above the predetermined fluid flow rate to be directed away fromsaid primary filtering element and through said secondary filteringelement while the amount of fluid at and below the predetermined fluidflow rate continues to pass through said metering orifice to saidprimary filtering element, said valve being contained completely withinthe manifold housing and not in direct communication with the outlet ora downstream side of the primary filtering element, wherein fluidfiltered in said primary filtering element and fluid filtered in saidsecondary filtering element is expelled through said outlet.
 8. Thefilter module assembly of claim 7 wherein the primary filtering elementhas a hollow, generally cylindrical configuration, and the secondaryfiltering element is a metal screen filter element, wherein the fluidflow rate responsive valve communicates between the inlet, the primaryfiltering element, and the secondary filtering element.
 9. The filtermodule assembly of claim 7 wherein the primary filtering elementincludes a perforated core and the porous filter medium is pleated, thepleated porous filter medium being disposed about the perforated core.10. A filter module assembly comprising: a manifold housing having aninlet for receiving a fluid to be filtered, an outlet for expelling thefluid, and fluid flow paths therebetween, said manifold housing beingattached atop a filter bowl; a primary filtering element and a secondaryfiltering element positioned in parallel to define a primary circuitfluid flow path and a secondary circuit fluid flow path respectively,the primary filtering element being contained within said filter bowl,and the secondary filtering element being contained completely withinthe manifold housing; and a fluid flow rate responsive valve forselectively directing at least a portion of the fluid away from theprimary filtering element and through the parallel secondary filteringelement, said valve being activated when a fluid flow rate through theinlet increases above a predetermined fluid flow rate, the amount offluid at and below the predetermined fluid flow rate continues to passthrough said valve to said primary filtering element and the amount offluid above the predetermined fluid flow rate being directed away fromsaid primary filtering element and through said secondary filteringelement, said valve being contained completely within the manifoldhousing and further including: a piston including a metering orifice, aspring, and a valve body of larger diameter than, and coaxial with, thepiston, the valve body including a plurality of first circularapertures, wherein the piston is slidably mounted within the valve body,the spring being biased in a first shape urging the piston into a firstposition within the valve body to close the piston over the plurality offirst circular apertures when the flow rate of the fluid is below thepredetermined fluid flow rate, and the spring being biased to allow thepiston to move away from the first position to allow the piston toexpose the plurality of first circular apertures when the flow rate ofthe fluid is above the predetermined fluid flow rate, the plurality offirst circular apertures then being in communication with the secondarycircuit fluid flow path, the amount of exposure of the plurality offirst circular apertures being proportional to the flow rate of thefluid, wherein fluid filtered in said primary filtering element andfluid filtered in said secondary filtering element is expelled throughsaid outlet.
 11. The filter module assembly of claim 10 wherein theprimary filtering element has a hollow, generally cylindricalconfiguration, and the secondary filtering element is a metal screenfilter element, wherein the fluid flow rate responsive valvecommunicates between the inlet, the primary filtering element, and thesecondary filtering element.
 12. The filter module assembly of claim 10wherein the primary filtering element includes a perforated core and theporous filter medium is pleated, the pleated porous filter medium beingdisposed about the perforated core.
 13. The filter module assembly ofclaim 10 wherein the filter medium of at least one of the filteringelements is pleated.
 14. The filter module assembly of claim 10 whereinthe filter medium of at least one of the filtering elements has ahollow, generally cylindrical configuration.
 15. The filter moduleassembly of claim 10 wherein the filter module assembly includes a highpressure relief valve.
 16. The filter module assembly of claim 10wherein the filter module assembly includes a bypass valve.
 17. Thefilter module assembly of claim 10 wherein the filter module assemblyincludes a device to measure pressure, temperature, and flow.
 18. Afilter module assembly comprising: a manifold housing having an inletfor receiving a fluid to be filtered, an outlet for expelling the fluid,and fluid flow paths therebetween, said manifold housing being attachedatop a filter bowl; a primary filtering element and a secondaryfiltering element positioned in parallel to define a primary circuitfluid flow path and a secondary circuit fluid flow path respectively,the primary filtering element being contained within said filter bowl,the secondary filtering element being contained completely within themanifold housing; and a fluid flow rate responsive valve for selectivelydirecting at least a portion of the fluid away from the primaryfiltering element and through the parallel secondary filtering element,said valve being activated when a fluid flow rate through the inletincreases above a predetermined fluid flow rate, an amount of fluid atand below the predetermined fluid flow rate continuing to pass throughsaid primary filtering element and an amount of fluid above thepredetermined fluid flow rate being directed away from said primaryfiltering element through said secondary filtering element, and saidvalve being contained completely within the manifold housing and furtherincluding: a piston including a metering orifice and a plurality ofcircular apertures, a spring, and a valve body of larger diameter than,and coaxial with, the piston, the valve body including a plurality offirst circular apertures and a plurality of second circular apertures,the plurality of circular apertures of the piston being in constantcommunication with the plurality of second circular apertures to furthercommunicate with the primary circuit fluid flow path to allow acontinuous flow of fluid below the predetermined fluid flow rate,wherein the piston is slidably mounted within the valve body, the springbeing biased in a first shape urging the piston into a first positionwithin the valve body to close the piston over the plurality of firstcircular apertures when the flow rate of the fluid is below thepredetermined fluid flow rate, and the spring being biased to allow thepiston to move away from the first position to allow the piston toexpose the plurality of first circular apertures when the flow rate ofthe fluid is above the predetermined fluid flow rate, the plurality offirst circular apertures then being in communication with the secondarycircuit fluid flow path, the amount of exposure of the plurality of thefirst circular apertures being proportional to the flow rate of thefluid, wherein fluid filtered in said primary filtering element andfluid filtered in said secondary filtering element is expelled throughsaid outlet.
 19. The filter module assembly of claim 18 wherein theprimary filtering element has a hollow, generally cylindricalconfiguration, and the secondary filtering element is a metal screenfilter element, wherein the fluid flow rate responsive valvecommunicates between the inlet, the primary filtering element, and thesecondary filtering element.
 20. The filter module assembly of claim 18wherein the primary filtering element includes a perforated core and theporous filter medium is pleated, the pleated porous filter medium beingdisposed about the perforated core.
 21. The filter module assembly ofclaim 18 wherein the filter medium of at least one of the filteringelements is pleated.
 22. The filter module assembly of claim 18 whereinthe filter medium of at least one of the filtering elements has ahollow, generally cylindrical configuration.
 23. The filter moduleassembly of claim 18 wherein the filter module assembly includes a highpressure relief valve.
 24. The filter module assembly of claim 18wherein the filter module assembly includes a bypass valve.
 25. Thefilter module assembly of claim 18 wherein the filter module assemblyincludes a device to measure pressure, temperature, and flow.